Copper (Cu) is a wiring material widely utilized in a BEOL (Back End of Line) of a semiconductor device such as an LSI. To form a Cu wiring layer, a barrier layer for suppressing diffusion of Cu into an insulating layer needs to be formed, and a seed layer for facilitating electrolytic plating of Cu also needs to be formed on the barrier layer by electroless Cu plating. Thus, a manufacturing cost increases. For the purposes of reducing the cost, aluminum (Al) of low cost is used as the wiring material at a portion where low electric resistance as low as that of Cu is not required.
In case of forming the Cu wiring layer connected to the Al wiring layer, the barrier layer needs to be formed to suppress Cu from being diffused into an ambient insulating layer which is made of a silicon-based material.
As a way to form the barrier layer on an inner surface of a deep hole such as TSV (Through Silicon Via) before burying the Cu wiring layer within the hole, there is known a method, such as PVD (Physical Vapor Deposition), using a film forming apparatus (see, for example, Patent Document 1). As another way to form the barrier layer on the inner surface of the deep hole, there is also known an electroless plating method. One of practical materials, which can be formed by the electroless plating method and have high barrier property against Cu, is cobalt or a cobalt alloy (hereinafter, referred to as “Co-based material”) (see, for example, Patent Document 2).
The present inventors have examined the application of Co-based electroless plating to the barrier layer for the Cu wiring layer connected to the Al wiring layer and has found out the following problems. A Co-based electroless plating liquid is alkaline and thus is capable of easily invading aluminum. Besides, the Co-based electroless plating liquid contains a complexing agent which is highly aggressive upon the aluminum. Thus, even if it is attempted to perform the Co-based electroless plating directly on the aluminum wiring layer, the underlying aluminum is first dissolved before the plating layer is grown. Thus, it is very difficult to form the Co-based plating layer on the aluminum wiring layer.
Patent document 1: Japanese Patent No. 4,246,706
Patent Document 2: Japanese Patent Laid-open Publication No. 2013-194306